The present invention relates to the field of computer and other networks; more particularly, the present invention relates to loopback cells for connection continuity detection within such networks.
Asynchronous Transfer Mode (ATM) or xe2x80x9ccell switchingxe2x80x9d is a method of transmitting digital information wherein the information is broken into equal sized units called xe2x80x9ccells.xe2x80x9d The individual cells of information are transmitted from a source node to a destination node through a xe2x80x9cconnectionxe2x80x9d. A connection, such as a Virtual Channel Connection (VCC), is a pathway through a digital network. A digital network is constructed of digital switches coupled together by digital communication links.
Each cell originates at a source node and is transmitted across the communication links. The communication links carry the cells of information between the digital switches along the VCC pathways. The digital switches route the cells from incoming communication links to outgoing communication links using connection routing tables. The routing tables receive cell addresses from an input VCC and are pre-programmed to map the cell to the appropriate output VCC using the cell address. The cell is subsequently transmitted to a destination node over the output VCC. Each digital switch can be connected to several communication links. Furthermore, each communication link can carry several different VCCs simultaneously.
FIG. 1 illustrates an exemplary digital switch node 100. Switch node 100 includes control processor 110, switch fabric 115, and interface modules 120 and 130. Switch node 100 relays ATM cells from its input ports to the appropriate output ports. Each port of switch node 100 is coupled to a communication link. Each communication link carries a multitude of VCCs.
Control processor 110 is configured to establish, modify and terminate virtual path connections coupled to switch node 100. Interface modules 120 and 130 receive ATM cells at ports of switch node 100 via VCCs. The interface modules also transmit cells to VCCs via the ports of switch node 100. Interface modules 120 and 130 include routing tables 123 and 133, respectively, for routing incoming cells to other switches. Although routing tables 123 and 133 are shown as independent entities, they may be components of a single routing table and need not be physically located on-board interface modules 120 and 130.
In a complex cell switching network, there are instances when the routing tables in the path of a connection may be misprogrammed. If a routing table is misprogrammed a discontinuity in a VCC path may be caused in one or both directions. Currently, a problem with discontinuous VCC paths can only be detected by end customers. The end customer must subsequently report the continuity problems to the service provider.
Upon learning of a continuity problem, the service provider must trace the path of the VCC to determine the location of the problem. A common method of determining the location of a problem is to connect to a digital switch with a network manager. As illustrated in FIG. 1, switch node 100 is coupled to network manager 180. One of the functions of network manager 180 is to communicate with control processor 110 in order to update routing tables 123 and 133. However, in the case, of misprogrammed routing tables, it may be necessary to ascertain which routing table and which entry in the routing table is misprogrammed.
Currently, continuity problems can not be detected before a network customer notices an outage. Thus, in order to determine the source of a continuity problem each connection or port must be manually placed in loopback mode. Consequently, network manager 180 must initiate the generation of Operations, Administration and Maintenance (OAM) loopback cells. After initiation by the network manager, OAM loopback cells are generated; for example at the interface modules, and transmitted over each connection until the misprogrammed path is found. Included in each OAM cell is a field that identifies the switch that generated the cell.
As the name implies, a loopback test involves the transmission of OAM cells between switches (or the nodes) of a network in a loop fashion, so that cells transmitted by a particular switch on a particular VCC are ultimately returned to that switch. Thus, if a transmitted OAM cell is received back at switch node 100, one can surmise that the particular connection on which the OAM cell was transmitted is operating without a discontinuity. However, if the OAM loopback cells are not received back at the digital switch, one can surmise there is a continuity problem with the VCC path. In the case where a misprogrammed routing table is involved, multiple switches may need to be tested before the source of the problem is located.
One problem with such manually initiated loopback tests is that a service provider must take a connection or port out of service while the test is being conducted. Accordingly, user traffic cannot flow on the connection. Often, a provider is not able to trace a problem after taking a single port out of service and it is not uncommon for a provider to have to take multiple connections or ports out of service in order to diagnose a particular problem. Further, since each switch may contain thousands of connections, it is not feasible to manually inspect each connection. Thus, in a complex cell switching network, manually testing each connection out of service is a very time consuming and error prone procedure.
An asynchronous transfer mode (ATM) switch is configured to automatically generate Operations, Administration and Management (OAM) cells for a loopback test at a first port whenever the first port is not receiving user data traffic from a first virtual connection associated with the first port. The ATM switch may include a switch management module which generates the OAM cells that are transmitted from the first port over the first virtual connection whenever a control processor initiates the loopback test.